Recently, there has been a strong demand for reduction in power consumptions and noise in a hermetic electric compressor for use in a domestic freezer and refrigerator or a room air-conditioner. For a reduction in power consumptions and a noise, an inverter-driven compressor is operated at a lower rotational speed (e.g. approx. 1,800 revolutions per minute (rpm) for a domestic refrigerator).
On the other hand, many lubricating oil pump systems for a hermetic electric compressor utilize a centrifugal force resulting from a rotation of a crankshaft because a lubricating oil reserved in the bottom of a hermetic shell is pumped up to upper sliding parts However, because the centrifugal force is proportional to the square of a rotational speed of a crankshaft, a power of pumping up oils is smaller as a rotational speed is lower. This causes a serious problem in the operation at a lower rotational speed.
A prior art is described hereinafter.
One of conventional hermetic electric compressors is disclosed in the Japanese Patent Unexamined Publication No. 1987-44108. FIG. 14 shows a sectional view of the conventional hermetic electric compressor. With reference to FIG. 14, a compressor body 500 is housed in a hermetic shell 501. In the hermetic shell 501, a frame 502 is disposed in the center, an electric motor 503 in the lower portion, and a compressing mechanism 504 in the upper portion. A crankshaft 505 penetrates through a bearing 506 of the frame 502. While the outer diameter portion of the crankshaft 505 is fixed to rotor 507 of the electric motor 503, an eccentric crankshaft 508 is engaged with a slider 510 of a piston 509 in the compressing mechanism 504 to perform a well-known compressing action.
Inside of the crankshaft 505, a slanting channel 511 having a relatively small diameter extends from the bottom end of the crankshaft 505 to the bottom end of a bearing 506. The slanting channel is opened to the outer periphery of the crankshaft 505 by a first lateral hole 512. A spiral groove 513 is formed on a portion of the crankshaft 505 inside of the bearing 506. The bottom end of the spiral groove is in communication with the lateral hole 512. At the top end of the spiral groove, the bottom end of a longitudinal hole 514 provided in an eccentric shaft 508 is opened to a thrust bearing sliding on a surface 515. At the same time, the bottom end of the longitudinal hole 514 intersects a second lateral hole 516. In other words, the crankshaft 505 is constituted so that the holes 512 and 516 are opened directly to the outer surface of the crankshaft 505. Additionally, at a bottom end 517 of the crankshaft 505, the slanting channel 511 is opened to a lubricating oil 518.
FIG. 15 is a detail sectional view of the bottom end 517 of the crankshaft 505 immersed in the lubricating oil 518. The lubricating oil 518 in the slanting channel 511 is formed into a free surface shaped like a parabola by a centrifugal force resulting from a rotation of the crankshaft 505. At this time, an ascending current 519 of the lubricating oil 518 sucked through the opening surface of the slanting channel 511 at the bottom end 517 of the crankshaft 505 is separated into two branches 520 and 521. A branch 520 is moved upwardly by the centrifugal force resulting from the rotation of the crankshaft 505. Another branch 521 slips in the vicinity of the bottom end of the slanting channel 511 and escapes through the opening surface of the slanting channel 511 out of the slanting channel 511. This branch 521 merges with the ascending current 519 sucked through the opening surface of the slanting channel 511 and flows into the slanting channel 511 again to form a short circuit.
In the constitution of such a prior art, the lubricating oil in the slanting channel 511 that directly extends from the bottom end of the crankshaft 505 diagonally to the top is immediately decentered by the centrifugal force only on the inner surface of the slanting channel 511 on the outer peripheral side, in a position slightly above the oil level of the lubricating oil 518 reserved in the lower portion of the compressor 500. Therefore, a force of lifting the lubricating oil is excellent. However, the ascending current 519 shown by the arrow, i.e. the lubricating oil that has been sucked through the opening surface of the slanting channel 511 at the bottom end of the crankshaft 505, is separated into the branches 520 and 521 each shown by the arrow. The branch 520 is moved upwardly by the centrifugal force. The branch 521 flows through the opening surface of the slanting channel 511 out of the slanting channel 511. This branch 521 merges with the ascending current 519 sucked through the opening surface of the slanting channel 511 and flows into the slanting channel 511 again to repeat short circuits. Repeating the short circuits is a major factor of the loss in the amount of the lubricating oil 518 flowing into the slanting channel 511. Further, because the centrifugal force is smaller at a lower rotational speed of the crankshaft 505, the rate of the branch 521 flowing out of the slanting channel 511 increases. This causes a drawback of delivering an insufficient amount of the lubricating oil to the sliding part in the upper portion.
Another hermetic electric compressor constituted to increase a centrifugal force for sucking an oil is disclosed in U.S. Pat. No. 5,707,220. However, this prior art has a complicated path of lubricating oil and a complicated constitution, and thus requires a large number of components. This causes problems of unstable supply of a lubricating oil and poor workablity in assembling.
Still another conventional hermetic electric compressor is disclosed in WO00/01949 Publication. This compressor employs a mechanical oil pump system in which the viscosity effect of lubricating oil pumps up a lubricating oil along a spiral groove between a stator having the spiral groove in the outer peripheral, surface thereof and a rotating sleeve. This system is highly reliable in ensuring an amount of supplied oil in a low-speed range (1,200 to 1,800 rpm). However, the constitution is extremely complicated and requires a larger number of components in comparison with an oil pump system using a centrifugal force. Therefore, this mechanical oil pump system has drawbacks of an expensiveness and a poor workability in assembling.
The present invention solves these conventional problems and aims to provide a simple lubricating oil pump system for a hermetic electric compressor that is capable of efficiently pumping up lubricating oil even at a low-speed rotation and has an excellent workablity in assembling.